1. Field of the Invention
The present invention relates to optics and, more specifically, to soft contact lenses.
2. Description of the Prior Art
Contact lenses are widely used for many different types of vision deficiencies. These include defects such as near-sightedness and far-sightedness (myopia and hypermetropia, respectively), and defects in near range vision usually associated with aging (presbyopia). Presbyopia occurs as a person ages when the lens of eye begins to crystalize and lose its elasticity, eventually resulting in the eye losing the ability to focus on nearby objects.
Some presbyopic persons have both near vision and far vision defects, requiring bifocal lenses to properly correct their vision. Many people prefer wearing contact lenses to correct their vision rather than bifocal eye glasses.
A typical single vision contact lens has a focus, which is the point on which parallel rays of light focus when the lens is placed perpendicular to the parallel rays, and an optical axis, which is an imaginary line drawn from the focus to the center of the lens. A posterior surface fits against the cornea and an opposite anterior surface has a vision surface that focuses light to correct the eye""s vision. In the case of a typical spherical lens, the vision surface has a single radius of curvature that is the distance from any point on the vision surface to a point on the optical axis referred to as the center of curvature. A bifocal lens has at least two vision surfaces on the anterior surface of the lens: a distance vision surface, for gazing at far off objects, and a near vision surface, for gazing at close objects (e.g., while reading).
Effective use of a bifocal contact lens requires translation of the eye between vision surfaces when the eye changes from gazing at an object at a distance to gazing at a nearby object. In such a situation, the pupil must move from being subtended by the distance vision surface to being subtended by the near vision surface.
Contact lenses generally are either hard lenses or soft lenses. Hard lenses tend to be less comfortable than soft lenses and, therefore, are usually worn for shorter periods of time.
While there are many designs for hard bifocal contact lenses, soft contact lenses have difficulty translating across the surface of the eye when the visual direction of the eye changes from horizontal gaze distance vision to down gaze near vision. This is due to the ability of a soft contact lens to conform closely to the shape of the cornea. For this reason, soft translating bifocal contact lenses are uncommon. Thus, users who desire bifocal contact lenses are usually limited to using the more uncomfortable hard lenses, while those who wish to wear soft contact lenses are usually limited to wearing monofocal lenses.
Therefore, there is a need for a soft bifocal contact lens that supports translation across the surface of the eye when the eye changes position from distance vision to near vision.
The disadvantages of the prior art are overcome by the present invention which, in one aspect, is a contact lens having top, a bottom, a rotational axis, an inner surface and an opposite outer surface, the outer surface including a plurality of zones. The plurality of zones include an optical zone, a ridge zone, a transition zone and a bevel zone. The optical zone has a lower edge, and includes a distance vision zone and a near vision zone.
The distance vision zone has a first radius of curvature that provides distance vision correction. The distance vision zone also has a first area that is sufficient to overlay a substantial portion of a pupil of a user and is disposed in a first position within the optical zone so that the user""s pupil is substantially subtended by the distance vision zone when the user is gazing at a substantially horizontal point.
The near vision zone is substantially concentric with the rotational axis and extends radially outward from the distance vision zone. The near vision zone has a second radius of curvature that provides near vision correction and has a second area that is sufficient to overlay a substantial portion of a pupil of a user. The near vision zone is disposed in a second position within the optical zone so that the user""s pupil is substantially subtended by the near vision zone when the user is gazing at a near vision point below the substantially horizontal point.
The ridge zone has an upper edge and a lower edge and is disposed below the optical zone. The ridge zone includes a latitudinal ridge portion that extends outwardly from the outer surface to enable engagement with a lower eyelid of a user and thereby provide vertical translation support for the contact lens when being worn by the user. The transition zone extends from the lower edge of the optical zone to the upper edge of the ridge zone and provides a smooth transition from the ridge zone to the optical zone.
In another aspect, the invention is a method of producing a master cast used in making a contact lens mold. A blank, having an outer surface, is rotated about a first rotational axis and at least one first surface is cut onto the outer surface of the blank.
The blank is also rotated about a plurality of secondary rotational axes, wherein each secondary rotational axis is different from the first rotational axis. A portion of a ridge-off surface is cut from the outer surface of the blank while it is rotating at each secondary rotational axis. Thus, a ridge-off surface is formed once the blank has been rotated about each of the plurality of secondary rotational axes.
These and other aspects of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the following drawings. As would be obvious to one skilled in the art, many variations and modifications of the invention may be effected without departing from the spirit and scope of the novel concepts of the disclosure.